mirror of https://github.com/facebook/rocksdb.git
57 lines
2.6 KiB
C++
57 lines
2.6 KiB
C++
|
// Copyright (c) 2011-present, Facebook, Inc. All rights reserved.
|
||
|
|
// This source code is licensed under both the GPLv2 (found in the
|
||
|
|
// COPYING file in the root directory) and Apache 2.0 License
|
||
|
|
// (found in the LICENSE.Apache file in the root directory).
|
||
|
|
//
|
||
|
|
// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
|
||
|
|
// Use of this source code is governed by a BSD-style license that can be
|
||
|
|
// found in the LICENSE file. See the AUTHORS file for names of contributors.
|
||
|
|
#include "table/block_based/block_prefetcher.h"
|
||
|
|
|
||
|
|
namespace ROCKSDB_NAMESPACE {
|
||
|
|
void BlockPrefetcher::PrefetchIfNeeded(const BlockBasedTable::Rep* rep,
|
||
|
|
const BlockHandle& handle,
|
||
|
|
size_t readahead_size,
|
||
|
|
bool is_for_compaction) {
|
||
|
|
if (!is_for_compaction) {
|
||
|
|
if (readahead_size == 0) {
|
||
|
|
// Implicit auto readahead
|
||
|
|
num_file_reads_++;
|
||
|
|
if (num_file_reads_ >
|
||
|
|
BlockBasedTable::kMinNumFileReadsToStartAutoReadahead) {
|
||
|
|
if (!rep->file->use_direct_io() &&
|
||
|
|
(handle.offset() + static_cast<size_t>(block_size(handle)) >
|
||
|
|
readahead_limit_)) {
|
||
|
|
// Buffered I/O
|
||
|
|
// Discarding the return status of Prefetch calls intentionally, as
|
||
|
|
// we can fallback to reading from disk if Prefetch fails.
|
||
|
|
rep->file->Prefetch(handle.offset(), readahead_size_);
|
||
|
|
readahead_limit_ =
|
||
|
|
static_cast<size_t>(handle.offset() + readahead_size_);
|
||
|
|
// Keep exponentially increasing readahead size until
|
||
|
|
// kMaxAutoReadaheadSize.
|
||
|
|
readahead_size_ = std::min(BlockBasedTable::kMaxAutoReadaheadSize,
|
||
|
|
readahead_size_ * 2);
|
||
|
|
} else if (rep->file->use_direct_io() && !prefetch_buffer_) {
|
||
|
|
// Direct I/O
|
||
|
|
// Let FilePrefetchBuffer take care of the readahead.
|
||
|
|
rep->CreateFilePrefetchBuffer(BlockBasedTable::kInitAutoReadaheadSize,
|
||
|
|
BlockBasedTable::kMaxAutoReadaheadSize,
|
||
|
|
&prefetch_buffer_);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
} else if (!prefetch_buffer_) {
|
||
|
|
// Explicit user requested readahead
|
||
|
|
// The actual condition is:
|
||
|
|
// if (readahead_size != 0 && !prefetch_buffer_)
|
||
|
|
rep->CreateFilePrefetchBuffer(readahead_size, readahead_size,
|
||
|
|
&prefetch_buffer_);
|
||
|
|
}
|
||
|
|
} else if (!prefetch_buffer_) {
|
||
|
|
rep->CreateFilePrefetchBuffer(compaction_readahead_size_,
|
||
|
|
compaction_readahead_size_,
|
||
|
|
&prefetch_buffer_);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
} // namespace ROCKSDB_NAMESPACE
|